Answer:
Helium
Step-by-step explanation:
An alpha particle is a particle that is emitted during radioactive decay.
The particle consists of two protons, and two neutrons.
The reason that an alpha particle can also be referred to as a Helium nucleus, is because the Helium atom consists of two protons, two neutrons, and two electrons. The nucleus only contains protons and neutrons, hence a Helium nucleus would consist of the same material as an alpha particle (two protons and two neutrons).